Young children can quickly learn the meaning of a new word after a brief, incidental exposure to the word and its referent, a process often described as "fast mapping". Little is known about the mechanism underlying this ability. More recent research reveals that this rapid learning ability is not specific to words; children, and adults, can quickly learn arbitrary facts about objects, and they rememember this information for a long time. The proposed research explores the nature and development of this learning capacity. The research investigates (1) the development of rapid learning about words and objects in the second year of life, and (2) the kinds of object properties that such children can learn rapidly and retain for extended periods. Finally, the research will begin to investigate the earlier ontogeny and phylogeny of these capacities through studies of pre-linguistic human infants and non-linguistic monkeys. The first series of studies compares 13- and 18-month-old infants' ability to learn about words and properties of objects. The next series of studies investigates the kinds of object properties infants are most adept at learning and remembering over time. A final series of studies examines whether fast mapping abilities are specific to language learners by testing pre-linguistic infants and non-linguistic monkeys.